It is known from the operationnal viewpoint, that such sensors must present, at the same time, a rapid response and the greatest possible precision within a large range of temperatures, of the order of 60.degree. to +250.degree. C.; in addition, from the point of view of construction, they should have a smooth surface, without joints and with a chemical resistance at least equivalent to the enamel covering the apparatus which they equip.
None of the devices known at present regroup all of these advantages.
Actually, to situate the state of the art, we can cite:
the system consisting of a thermocouple welded in an enamelled base: even though its response time is short, its precision is weak. Also it is not interchangeable.
the system consisting of a thermocouple or a resistance thermometer plunged into oil inclosed in a bulb: this one is interchangeable, but in this case, the thermal inertia of the system renders its response time too long.
the system consisting of a thermocouple or a resistance thermometer inside a coating of enamel: in this case, the response time is very short, but the realization is difficult, and it is not interchangeable, except by changing the whole enamelled part.
the system consisting of the sensor inserted in a cone glued by enamelling into a receptacle provided in the wall of the apparatus, it is not dismantable.
Systems are also proposed which are mounted from the interior of the apparatus, with the interposition of a teflon gasket. Such an assembly, as it is defined, represents in itself an inconvenience, since it does not allow for removal from the exterior of the apparatus, in this case it is not entirely enamelled.